Multiple-spindle automatic screw machines (e.g., Davenports, Acme, etc.) have long been the world's primary means for forming and cutting off small parts (e.g., screws, bolts, pins, etc.) from the ends of workpieces of long bar stock (cylindrical metal bars). Such automatic screw machines have multiple spindles (which each receive and hold a respective bar stock workpiece), and they have automatic cyclical drives that serially feed and position the distal end of each workpiece bar in a respective one of the work-holding spindles.
The screw machine's automatic operations also serially index the spindles relative to a plurality of sequential tool-holding work stations. At the first work station, the distal end of each workpiece bar is serially fed to a pre-shaping location within its respective work-holding spindle so that a distal end portion of the bar projects beyond the face of the spindle a predetermined distance. Thereafter, at each successive work station, each spindle holds and/or rotates its respective workpiece while a respective tool, which is adjustably mounted at each work station, shapes a portion of the rotating workpiece. As the spindles index through each successive work station, the distal end portion of each bar workpiece is formed into a desired product having specified dimensions. At a final work station, the product is separated from the workpiece bar; and as the machine is indexed once more, a new length of workpiece is fed into the spindle which is then returned to the first work station to begin the formation of another part.
The inadvertent manufacture of "short parts" (improper length) has been a chronic problem for the operators of such machines since their inception nearly a hundred years ago. That is, parts having a length that is less than a predetermined minimum requirement may be turned out by the hundreds before the operator notes that the machine is producing such an unacceptable product. However, with recent "zero defect" quality control requirements for parts suppliers, the production of even a single short part can expose the part manufacturer to returns and complaints and, more importantly, can affect consumer safety in many applications.
Very sophisticated and accurate part cutting machinery is well known, and all include very complex measuring apparatus for determining part accuracy. For example, such complex measuring apparatus often comprise specially constructed position probes (e.g., see U.S. Pat. No. 5,001,464 to Tanaka), optical encoders (e.g., see U.S. Pat. No. 5,310,064 to Neff et al.), sophisticated electronic circuitry, etc. These known prior art part measuring systems are all relatively expensive to install; difficult to set up; and, for generally unattended automatic screw machines, impractical to use.
The invention disclosed herein is a simple and relatively inexpensive accessory which can be readily affixed to existing standard (unsophisticated) screw machines for overcoming the chronic and expensive "short part" problem.